This invention relates to a gas turbine combustor which can prevent the burning of premixed flame-formation nozzles by the back flow of a fuel gas.
A diffuse combustion system, in which fuel and the air are ejected from different nozzles and burned, has been often used for conventional gas turbine combustors. Recently, however, a premix combustion system which is more advantageous in the reduction of thermal NOx has been also used in place of the diffuse combustion system. The premix combustion system means that fuel and the air are premixed with each other and the mixture is ejected from the same nozzle and burned. According to this combustion system, even if fuel is rarefied, it is possible to burn the fuel in that state in any combustion regions. Therefore, it is easy to decrease the temperature of the premixed fuel and advantageous in the reduction of NOx compared with the diffuse combustion system. On the other hand, this premix combustion system has the following problem. That is, since the air is excess compared with the fuel and the temperature of premixed flames is low, the stability of a combustion state is inferior.
Recently, there is known a technique which employs spread flames formed by reacting pilot fuel with the air, as pilot flames so as to solve the above-stated problem and to maintain a stable combustion state while the fuel is rarefied in the premix combustion system. Specifically, this technique is for igniting premixed gas using high-temperature combustion gas discharged from spread flames and stabilizing the premixed flames in the premix combustion system. A gas turbine combustor using this technique is referred to as multi-nozzle premix type gas turbine combustor.
FIG. 7 is a front view of a multi-nozzle premix type gas turbine combustor which has been conventionally used. In addition, a cross-section in an axial direction of the conventional gas turbine combustor is similar to the cross-section depicted in FIG. 8. However, the conventional premixed flame-forming nozzles 40 are used instead of premixed flame-forming nozzles 41. A combustor inner cylinder 20 is provided in a combustor outer casing 10 with a certain clearance kept between the combustor outer casing 10 and the combustor inner cylinder 20. A spread flame formation cone 30 which forms spread flames is provided on the central portion of the combustor inner cylinder 20. The spread flame formation cone 30 causes pilot fuel supplied from a pilot fuel supply nozzle 31 to react with the air supplied from the portion between the combustor outer casing 10 and the combustor inner cylinder 20 and forms spread flames.
Eight premixed-flame formation nozzles 40 which form premixed flames are provided around the spread flame formation cone 30. Premixed gas is formed by mixing the air supplied from the portion between the combustor outer casing 10 and the combustor inner cylinder 20 with main fuel and then ejected from the premixed flame-formation nozzles 40. The premixed gas ejected from the premixed flame-formation nozzles 40 is ignited by high-temperature combustion gas discharged from the spread flames to thereby form premixed flames. High-temperature, high-pressure combustion gas is discharged from the premixed flames. The combustion gas is passed through a combustor tail pipe (not shown) and then introduced into the first-stage nozzle of a turbine.
In the meantime, since the outlets of the conventional premixed flame-formation nozzles 40 are elliptical, the clearances between the adjacent premixed flame-formation nozzles 40 are not constant as shown in FIG. 7. Therefore, the high-temperature combustion gas discharged from the premixed flame flows back because of uneven air flows between the wide clearances and the narrow clearances. Portions on which the premixed flame-formation nozzles 40 are adjacent each other (the side surface portions of the premixed flame-formation nozzles 40 adjacent each other in the peripheral direction of the combustor inner cylinder 20) are, in particular, disadvantageously, greatly burned.
To avoid the burning, it may be possible to arrange the premixed flame-formation nozzles 40 to keep a certain distance from one another so as to prevent the combustion gas from flowing back. However, if the number of the nozzles arranged as stated above is small or many nozzles are to be arranged as stated above, the size of the combustor itself becomes disadvantageously large.
It is an object of this invention to provide a gas turbine combustor which can prevent the burning of premixed flame-formation nozzles due to the backflow of high-temperature combustion gas.
In the conventional gas turbine combustor, since the clearances between the outer peripheries of the adjacent premixed flame-formation nozzles are not constant, most of the cooled air flows out from the portions between the adjacent premix nozzles and the combustor inner cylinder and the like.
In the gas turbine combustor according to one aspect of the present invention, the nozzle outlet of the premixed flame-formation nozzles are shaped so that the clearances between the outer peripheries of the adjacent premixed flame-formation nozzles have same dimensions at the nozzle outlets. Therefore, the cooled air flows even into the portions between the adjacent premixed flame-formation nozzles. As a result, it is possible to suppress combustion gas from flowing back to the portions between the adjacent premixed flame-formation nozzles and to prevent the portions between the adjacent premixed flame-formation nozzles from being burned.
In the gas turbine combustor according to another aspect of the present invention, sealing members which are provided between the premixed flame-formation nozzles adjacent each other, respectively make the clearances between the premixed flame-formation nozzles adjacent each other have same dimensions at nozzle outlets. Therefore, the cooled air flows even into the portions between the adjacent premixed flame-formation nozzles, thereby making it possible to suppress the backflow of combustion gas into these portions. As a result, it is possible to prevent the portions between the adjacent premixed flame-formation nozzles from being burned.
In the gas turbine combustor according to still another aspect of the present invention, by providing the sealing members in the generally triangular spaces, clearances of almost same dimensions are generated between the outer peripheries of the premixed flame-formation nozzles. Therefore, most of the cooled air is passed through the clearances, so that it is possible to suppress combustion gas from flowing back to the portions between the adjacent premixed flame-formation nozzles and to prevent the portions between the adjacent premixed flame-formation nozzles from being burned.
In the gas turbine combustor according to still another aspect of the present invention, the inside of the combustor inner cylinder and the outside of the spread flame formation cone are shaped to be matched to the outer shape of the annular premixed flame-formation nozzle groups with same dimensions, respectively. Therefore, the cooled air evenly flows into the peripheries of the premixed flame-formation nozzles. It is, therefore, possible to suppress the backflow of combustion gas in the direction of the adjacent premixed flame-formation nozzles. As a result, it is possible to prevent the portions between the premixed flame-formation nozzles from being burned.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.